1. Field of the Invention
This invention relates to a control apparatus for sewing machine, and more particularly to a control apparatus for industrial sewing machine with automatic needle stopping means.
2. Description of the Prior Art
Recently, control apparatus with sequence control for use in industrial sewing machines have been developed.
For convenience of explanation, a co-ordinate system is assumed in which the ordinate represents the rotational speed N of a sewing machine shaft driven by a motor and abscissa represents time. A sewing machine is started and operated at a high speed N.sub.H. If the sewing machine is provided with a deceleration command, the motor is disconnected from a power source and a brake is actuated to facilitate the deceleration of the sewing machine. When the speed falls to a predetermined low speed N.sub.L at time (second) after the provision of the deceleration command, the braking action is loosened and the low speed N.sub.L is retained till time (second) for positioning. As the sewing machine needle travels and reaches a specified position, for example, low position, the position detector unit is so actuated as to energize an electromagnetic brake. The electromagnetic brake is slightly delayed to operate on account of its inherent time lag and it causes the sewing machine needle to stop at the low position. Then, the sewing machine is reactuated at the low speed by a command from an operator. While the sewing machine needle travels from the low position to the high position, a thread is automatically cut off. The sewing machine needle is stopped at the high position and one sewing cycle is completed.
Many sewing machine control apparatus performing such control mode employ a command circuit incorporated with a number of control elements, for example, flip-flops. Therefore, these control apparatus are sensitive to noises and prone to erroneous operations, giving rise to impairment of reliability. Besides, they are complicated.